1. Field of the Invention
The present invention generally relates to a camera lens module and more particularly, a camera lens module for controlling a focal length by moving a lens housing along an optical axis.
2. Description of the Related Art
A digital camera is a device for electrically performing signal processing including recoding, processing, and reproduction by converting an image signal to an electrical signal. Compared to a silver halide film-type camera, the digital camera enables a user to view a captured image immediately without the need for development or chemical processing. Also, since recorded image information exists in an electronic form, the digital camera allows computer-aided post-processing and remote transmission of an image. This explains the popularity of the digital camera as one of image apparatuses for the multimedia era.
Recently, the digital camera has found its use in a portable terminal by mounting a camera lens module in the portable terminal. As portable terminals are equipped with camera lens modules that perform almost as well as the standard digital camera itself users generally see no distinction between the digital camera and the portable terminal with a camera lens module.
However, to be included within a portable terminal, the camera lens module must become smaller. Thus, a challenging issue for the camera lens module is that it should perform well despite its small size. Resolving power as well as magnification is critical to the performance of the camera lens module. With an improved resolving power, an image of an object is rendered in such clarity that minute details of the image can be observed. The camera lens module can select a focal length by controlling the distance between an image sensor and a lens and the optimal focal length offers the maximum resolving power that the camera lens module can exert.
FIG. 1 is an exploded perspective view of a conventional camera lens module 200.
Referring to FIG. 1, the camera lens module 200 includes a lens housing 201 and a main frame 202. The lens housing 201, which is configured as to be combined with the main frame 202, includes a lens (not shown) and an infrared filter (not shown) therein. The lens housing 201 is also provided, on an outer surface, with a first engagement portion 211 having screw threads. The main frame 202 has an image sensor (not shown) mounted therein and is provided with an engagement hole 221 for containing the lens housing 201 therein. The engagement hole 221 has a second engagement portion 223 with screw threads on an inner surface thereof, for combining with the first engagement portion 211. When the lens housing 201 is mounted in the main frame 202, the second engagement portion 223 is screw-engaged with the first engagement portion 211. At the same time, the lens and the infrared filter are aligned with the image sensor along an optical axis. With the first and second engagement portions 211 and 233 in screw engagement, the lens housing 201 can move along the optical axis, rotating in the engagement hole 221, thereby adjusting the distance to the image sensor. Thus, the camera lens module 200 sets a distance between the lens and the image sensor according to a back focal length specific to the lens mounted in the lens housing 201. Setting the distance between the lens and the image sensor according to the back focal length of the lens will be referred to as control of an initial focal length.
With the initial focal length set, the camera lens module 100 controls the distance between the lens and the image sensor according to the distance between an object and the lens by use of an actuator (not shown), when the object is actually captured.
In the process of controlling the initial focal length, the screw threads formed in the lens housing and the main frame increase the size of the camera lens module by as much as their height and, thus, impeding miniaturization of the camera lens module. Moreover, foreign materials are produced due to friction involved in the screw engagement between the lens housing and the main frame. The foreign materials may fall onto the infrared filter or the image sensor and taking the form of an image in a captured image. As a consequence, the quality of the captured image and the reliability of the camera lens module are decreased.